Thermal stability and wear behaviour of AISI S2 tool steel processed by Laser Powder Bed Fusion

Abstract

This study investigates the thermal stability and wear behaviour of AISI S2 tool steel processed by Laser Powder Bed Fusion. The processability of this material was previously examined in a separate study conducted by the same team. Isothermal treatments up to 10 hours were performed on as-built samples at three different temperatures (200 °C, 300 °C, and 400 °C), in order to investigate the thermal stability. The alloy is thermally stable at 200 °C and 300 °C, whereas its microstructure and properties change at 400 °C. Pin-on-disc campaigns were conducted at room and high temperatures. The wear sequence of the material at room temperature was elucidated, following the approach of interrupted wear tests. High-temperature wear tests were conducted at the same temperatures as those of the isothermal treatments. The wear behaviour at 200°C and 300°C were found to be similar to that at room temperature, while the wear behaviour at 400 °C was markedly different, including the formation of a thick oxide layer and of a tribolayer that protect the surface from further wear. The results showed an increased wear rate at high temperatures compared to that at room temperature. These analyses were conducted using optical and scanning electron microscopy, DSC, pin-on-disc, profilometer, and macro and nano-indentation techniques.